Solar or photovoltaic cells are manufactured by depositing conductive inks in desired patterns on the tops and bottoms of a solar cell wafer. The wafers are thermally processed in a furnace system to dry the conductive ink and burn off binders and other materials after which the materials are fired to form metallization patterns on the wafer surfaces. Furnace systems for such metallization processes typically employ infrared heating lamps to provide the rapid thermal processing environment needed for processing the wafers.
Known wafer firing furnaces can be generally characterized as comprising three sections: a drying zone at an entrance where the wafers are loaded into the furnace; a burnout/firing zone, generally thought of as the middle zone; and a cooling section located at the end and having an exit from which the wafers are removed. In some wafer firing furnaces, a single-belt conveyor is used to move the wafers through the sections and, therefore, the wafers move through each section at the same speed. Alternatively, multi-belt structures are known where a separate belt runs through each section, allowing for variations in belt speed depending upon the section.
It is known that the wafer should be quickly cooled after it has reached its maximum temperature in order to assure highest quality wafers. Known ovens, however, cause a heated wafer to dwell at this high temperature because of the time necessary to transfer the wafer from the burnout/firing zone to the cooling zone.
What is needed is a wafer processing furnace that provides for minimal dwell time at temperature along with a very fast cooling profile.